Conventional mechanical seal assemblies are employed in a wide variety of environments and settings, such as for example, in mechanical apparatuses, to provide a fluid-tight seal. The sealing assemblies are usually positioned about a rotating shaft or rod that is mounted in and protrudes from a stationary mechanical housing.
Split mechanical seals are employed in a wide variety of mechanical apparatuses to provide a pressure-tight and fluid-tight seal. The mechanical seal is usually positioned about a rotating shaft that is mounted in and protruding from a stationary housing. The seal is usually bolted to the housing at the shaft exit, thus preventing the loss of pressurized process fluid from the housing. Conventional split mechanical seals include face-type mechanical seals, which include a pair of sealing rings that are concentrically disposed about the shaft, and axially spaced from each other. The sealing rings each have sealing faces that are biased into sealing contact with each other. Usually, one seal ring remains stationary, while the other ring contacts the shaft and rotates therewith. The mechanical seal prevents leakage of the pressurized process fluid to the external environment by biasing the seal ring sealing faces in sealing contact with each other. The rotary seal ring is usually mounted in a holder assembly which is disposed in a chamber formed by a gland assembly. The holder assembly may have a pair of holder halves secured together by a screw. Likewise, the gland assembly may have a pair of gland halves also secured together by a screw. The sealing rings are often divided into segments, each segment having a pair of sealing faces, thereby resulting in each ring being a split ring that can be mounted about the shaft without the necessity of freeing one end of the shaft ends.
Prior split mechanical seals have rotary and stationary components assembled around the shaft and then bolted on to the equipment to be sealed. A rotary seal face is inserted into a rotary metal clamp after the segments are assembled around the shaft. Then, the stationary face segments and gland segments are assembled and the split gland assembly is then bolted to the pump housing.
Previous split mechanical seal designs posed several problems. A first problem with prior split mechanical seal designs relates to the insertion of the rotary seal ring into the holder assembly that is clamped around the shaft. An O-ring seals the rotary seal face to the clamped holder in an axial direction. The rotary seal face must be pushed into a tight space inside the clamped holder, and some difficulty may often be encountered. The elastomeric O-ring sealing the rotary seal face to the holder needs to be compressed for sealing, and a certain amount of force is required to insert the seal face inside the clamped holder. In addition, since the O-ring tends to grab the seal ring and inhibits sliding, the rotary seal face of prior art mechanical seal assembly designs has a tendency to “pop-out” after being inserted. Further, the movement of the O-ring when installed can result in the O-ring being disposed in an angled position, rather than a more preferred vertical position relative to the rotary seal ring. From the angled position, the installer would be required to move the O-ring back to the original position, which is difficult. This process can require several attempts during installation to have the rotary seal face properly seated inside the clamped holder.
Another important consideration is to maintain perpendicularity of the rotary seal face to the shaft for smooth operation. It is quite possible to have one side of the rotary seal face further inside the clamped holder than the other side. The result is an out-of-squareness condition of the rotary seal face with respect to the shaft axis. This in turn creates a back and forth motion of the stationary seal ring as it tilts from side to side in order to track the rotary seal ring with every shaft revolution. If significant enough, this can result in shortened seal life.
Another problem experienced with prior split mechanical seal designs occurs when excessive torque is applied to the gland bolts while tightening the seal gland to the pump or other equipment housing. This problem is most severe when only two gland bolts are used. Since two and four bolt configurations are the most common bolt designs, bolt slots are typically not provided in an even symmetrical location with respect to the gland splits. Indeed, when two bolts are used the most logical bolt location would be to have them located 90 degrees from the split. If this were done, however, when four bolts are used, the other two bolts would be located right at the split, which is undesirable. To avoid this design occurrence, the slots are located anywhere from about 15 to 45 degrees from the split line.
Therefore when only two bolts are used for the gland assembly, the loading on the gland halves is not symmetrical or even with respect to the split plane. The face gasket which is compressed between the gland and the housing is typically of an elastomeric material which is resilient enough to provide a seal. Given the uneven nature of the clamping load, the bolting force must be transmitted on each side of the split by the joining mechanism of the gland halves. These are typically an alignment pin and a securing screw tangential to the shaft outer diameter (compared to the axial direction of the gland bolts). The alignment pins are quite small in relation to the forces applied, and therefore cannot ensure that the gland halves will not slide against each other thereby distorting the alignment pin and the gland halves. The result is twofold: first there is a reduction in sealing ability of the gaskets between the gland halves, and second, there is an out-of-round twisting of the gland assembly which creates sealing problems with the stationary seal ring.